A number of plastic containers that are now used, for example, plastic flasks and the like—are produced in a stretch blow-molding process. In this method, a so-called preform—which can have an elongated, tube-like shape and a base on one longitudinal end and a neck area with formed threaded sections or the like on the other longitudinal end—is inserted into a mold cavity of a blow mold and blown in through a medium that is injected with overpressure. In this case, the preform can be additionally elongated in the axial direction with an elongated mandrel that is run in through the neck opening. After the elongation/blow-molding process, the finished plastic container is demolded from the blow mold.
A single- or multi-layer preform can be produced in a separate injection-molding method before the stretch blow-molding process. It has also been proposed to produce preforms in a plastic extrusion press method. As raw material for the production of plastic containers in the stretch blow-molding process, polypropylene or PET (polyethylene terephthalate) can be used. Polypropylene and PET have been tested multiple times, and their properties are adequately known. In the so-called single-stage stretch blow-molding process, the preform is inflated and elongated directly after its production to form a plastic container. In some cases the plastic containers can be produced in a two-stage method at a different place and time from the stretch blow-molding process and can be intermediately stored for later use. In the later stretch blow-molding process, the preforms are heated again, introduced into a blow mold, stretched with an elongated mandrel in the longitudinal direction, and inflated according to the mold cavity by overpressure to form a plastic container. In this way, both processes—the injection-molding and the stretch blow-molding—can be operated separately and optimally.
The preforms that are used in the stretch blow-molding method can have an elongated shape and a convex base that is curved outward. The neck area of the preform can be already completely formed and can be provided with threaded sections or similar positive protrusions, which make it possible to attach a closure or cover, which can be equipped with correspondingly designed locking elements. In the two-stage process, the preforms can be heated again to their deformation temperature range before the stretch blow-molding. To this end, the preforms can be plugged with their neck areas into finger-like holding devices and transported through a heating station. In some cases, the heating of the preforms can be carried out via infrared radiation or near-infrared radiation, which can be generated by quartz tube radiators. For better use of the energy emitted by the quartz tube radiators, one or more mirrors can be provided that reflect the electromagnetic radiation. In the heating station, the preforms are transported between the quartz tube radiators and the mirrors facing them.
Through the bomb-shaped base of the preform, the irradiated infrared radiation can travel by scattering or directly to the finger-like holding devices of the preforms, which can thus be heated. To prevent deformations of the neck area of the preform that can be formed with high accuracy, the finger-like holding devices can be cooled. Because the absorbed irradiated energy often cannot be drained off to a sufficient extent even by the cooling of the holding devices, the preform neck can be designed with a relatively larger wall thickness than would be necessary for the plastic container that is to be manufactured from the preform. During stretch blow-molding, the preform can be stretched longitudinally using an elongated mandrel. In the area of the support surface of the base of the preform with the elongated mandrel, the base can cool relatively quickly, and an undesirable accumulation of amorphous material can occur in the base area of the plastic container that is produced in the stretch blow-molding process.